1. Field of the Invention
The present invention relates generally to image sensing devices, and more specifically to a two-dimensional charge-coupled device (CCD) image sensor of the progressive scan format.
2. Description of the Related Art
The use of input devices such as digital still cameras for personal computers requires scan conversion from the interlace format to the noninterlace (progressive) format since most of these input devices are implemented with components used in the standard television systems, whereas the display system of computers is implemented with the progressive format. In order to eliminate the need for the scan conversion, the progressive scan format is increasingly adopted by current CCD (charge-coupled device) image sensors.
To implement the progressive scanning in an interline CCD image sensor, three-phase clock pulses must be used to transfer charge packets of two-dimensional image along vertical charge transfer means or CCDs to a horizontal CCD. However, one disadvantage of the three-phase transfer mode is that polysilicon electrodes must be arranged in a three-layered structure since it involves an added manufacturing step as compared with the two-layered structure of the transfer mode employed in the interlace scanning.